"Many worlds has a physical basis to it" has no physics-meaning that I can discern. In order to have one, it would have to deviate from the other isomorphisms and cease to be an isomorphism, and thus somehow be testable, which it isn't. (My previous post is word salad to some extent too, since I'm jamming it into an HN post. But the core insight there is basically, let the math be the math and stop imposing your globally-based ideas on the local world.)

It would have a "physical basis" to it if you could visit the alternatives somehow, in which case they could be demonstrated to physically exist and all doubt would be removed. But so far that is not on offer.

Pretty much. Seems that the "shut up and do the math" QM interpretation is still the important one